Thirty buildings in the district are constructed of brick; the rest are frame. There are no stone buildings.

Residential structures currently account for approximately 86% of the buildings in the district. Nine percent (9%) support commercial activities, while 3% are used by religious organizations, and 1% serve municipal functions.

The process of defining the boundaries of the Delaware City Historic District involved reviewing the results of an existing architectural survey of the town and examining these buildings and their relationship to each other in the field. The survey was conducted by the Delaware City Area Historical Society in 1979 and 1980 under the general direction of Richard Hendricks, their president. All of the buildings bounded by Fifth Street, the canal, the Delaware River, and Monroe Street were inventoried, including modern and substantially altered structures.

Since Delaware City's architectural development reveals many significant building periods and styles dating from 1827 well into the twentieth century, contributing structures within the district are defined as all pre-1933 buildings that possess sufficient integrity so that their scale, massing, fenestration, and details convey the character of their particular period of significance. The pivotal structures that illustrate the major areas of significance possess a very high degree of integrity. While a good number of the less individualistic buildings that contribute to the district have been altered somewhat by the addition of rear wings, modern siding, or replacement windows, they do possess the essential form and style of their period, and in terms of significance they reveal the popularity of various styles and the relationship of building forms that the pivotal structures alone cannot convey.